Instructables

Power LED from RF?

I have a maybe somewhat unusual question.There is a super simple circuit that enables an LED to be powered by ringing mobile phone.
Can be found at http://www.creative-science.org.uk/mobile_LED_simple.html
What I would like to do is to power LED but from a distance, preferably Radio Stations of (if possible) power lines.
LED does not have to be constantly on or bright, it can "blink".
I was looking at Joule Thief and combining it with capacitor ...

The point is that there should be no battery.
Is such a thing possible?

Yes it is possible. In the UK in the early 90's we had mobile phones with fancy 5 LED antennas that would just slot into the antenna socket replacing the old antenna. Inside were 2 diodes for rectification and 5 led's and a couple of caps and a small coil of wire acting like an inductor. It would flash just prior to the phone ringing and then brightly rotate the colours randomly with the signal all the time you were in conversation or the mobile was used. And it was very bright as the LED's were just 1mm and the draw was very low (perhaps 4mw per LED).Obviously the mibile signal was very low wattage and the antenna was as close to the source as could be and a big but the telephone was of course an analogue signal but none the less free light from RF. I so wish I still had one to demonstrate.
nccwarp9 (author)  CodfishCatfish1 year ago
something like
http://lamye.en.alibaba.com/product/359660351-213184655/LED_Mobile_flash_sticker.html

???

Re-design3 years ago
I doubt that you could ever get enough current from the air waves to power an led. The amount available if extremely small, even when using huge antennas. Radio works by using very sensitive devices and amplifying the current to a usable level.
nccwarp9 (author)  Re-design1 year ago
There are examples of running a, a believe a pieze speaker

http://sci-toys.com/scitoys/scitoys/radio/radio.html

shouldn't there be enough power to light a small led ?
No. I you read the whole bunch of articles, you'll see that he put meters on one of the radios with a long antenna and only got 125 millivolts and 175 microamps and that's using a 200 ft. antenna.

I'm not saying that there is no power to be gotten from the airwaves just not in the amount it would take to do any real work like lighting an led.

Really nice radios that have lots of sensitivity and sound power may have 2 RF amps and 2 or 3 audio amps to get the sound power up.  And compared to a light bulb or small motor, a speaker really doesn't take all that much power to run.
Oh and if your not convinced then you only need to stand next to a CB antenna with a florescent tube to see it will glow quite bright. Recently a whole field was filled with florescent tubes under a power line to demonstrate the lethal effects of strong EMF. It was all about cancer from power lines. Power-lines also use a balanced signal.
http://www.youtube.com/watch?v=cXhZvyGtMrk
Only if you are prepared to wait for a very long time before you can get an LED to flash. The energy has to come from somewhere, and the amount you receive varies with the square of distance from the source.

Steve
nccwarp9 (author)  steveastrouk3 years ago
Long as in minutes, hours, days ??
Depends on the quality of tuning, and the distance to the source. Any of the above. Stealing RF energy has been done before, but generally only in very very close proximity to the source antenna. One guy in the UK many years ago was convicted of stealing electricity near a very strong LW source, by dint of adding rectifiers to his house wiring !

Steve
seandogue3 years ago
(removed by author or community request)
nccwarp9 (author)  seandogue3 years ago
Something like ... ??

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=HLMP-P156-EG031-ND